Major Essay A common theme through the unit has been the controversial or conflicting findings and their impact on the understanding of neuroendocrinology. Using material from lectures, journal club...

MAJOR ESSAY ON KISSPEPTIN
Table of Contents
Introduction    3
Criticality of Kisspeptin for the onset of puberty    3
Direct signalling of satiety hormone leptin to kisspeptin neurones    4
Significance of kisspeptin in obesity and energy balance    6
Conclusion    7
References    8
Introduction
Kisspeptin is a neuropeptide that was identified as the product of the suppressor gene of metastasis that accounts for malignant melanoma. This protein is an endogenous ligand that acts as a G-protein coupled receptor. Distribution of this protein is described mainly in rodents as there they can bind with the receptors present in placenta as well as presence in a large amount in central nervous system. Kisspeptin is abundantly expressed in arcuate nucleus (Arc) and anteroventral periventricular nucleus of forebrain and it basically expresses oestrogen and androgen receptor. Hence, it targets mainly for the gonadal steroid in both male and female. Kisspeptin signalling helps to mediate the neuroendocrine processes that are triggered in puberty. In this essay, the role of kisspeptin has been described in the onset of endocrinology. Signalling of leptin hormone to kisspeptin is also described with the role of the protein in obesity and importance in energy balance.
Criticality of Kisspeptin for the onset of puberty
The kisspeptin receptor is GRP54, the ligand is Kiss1 that are present in uppermost level in central nervous system, and placenta helps in the process of puberty. According to Araujo-Lopes et al. (2014), a mutation occurred in the gene of kisspeptin, which resulted a receptor that cause infertility. This protein acts with the help of the receptor of the gene itself and regulate the reproductive axis while it stimulates the hormone hypothalamic gonadotropin hormone. It was also found that two other neuropeptides named neurokinin B and dynorphin that share their role in association with kisspeptin as an important hypothalamic regulator that acts on reproductive function. These proteins are secreted together with kissprotein that ultimately regulates gonadotropin hormone secretion.
Kisspeptin is the family of protein that is derived from a differential proteolysis from a common precursor. According to Dubois et al. (2015), reports also reveal the presence of kisspeptin product in pancreas, small intestine, adipose tissue, testes, aorta and peripheral blood lymphocyte. Assay by hybridisation process in mice tissue reveals the presence of kisspeptin neurones that are numerous in Arc nucleus. Deletion of GPR54 gene causes mutation that is paired with sexual maturation, which suggests the signal of the gene kisspeptin is essential for puberty. Administration of exogenous kisspeptin initiates a number of aspects of puberty as LH release or the opening of vagina. Neural KISS1 expression increases in case of pre to post puberty, though, a specific population of KISS1 changes with the difference of puberty period and it differs from primate to rodents.
As per the idea of Garcia et al. (2018), the change in KISS1, activity presents a common event in the time of puberty. These findings show the hypothalamic derived product of kisspeptin gene GPR54; the signal of this gene is involved with the mechanism, which ultimately helps in the initiation puberty. However, this process and mechanism is still in mystery. It was found that the protein helps to trigger the release of the sex steroid that is released from gonads, which have a positive feedback on the KISS 1 neuron. The expression of this neuron in AVPV nucleus puts a negative feedback on the arcuate nucleus of neurons.
According to Han et al. (2015), it was found that the suppression this kisspeptin when performed using the sex steroids was appeared occur by the receptors of oestrogen in female as well as in oestrogen receptor that is ER. In case of male, androgen receptors perform the same work and all the cells of AVPV in both the male and female express oestrogen receptor. This suggests that these neurons gives a tonic to GnRH neuronal activity that is regulated by the negative as well as positive feedback that is affected by gonadal steroids; testosterone in male and oestradiol in female. The role of this protein kisspeptin in oestrous cycle and puberty occurs when a stimulation of gonadotrophic hormone occurs that involves the positive feedback between oestrogen, LH and GnRH as well as their regulation that triggers the oestrous cycle. In hypothalamus, the mRNA expression of kisspeptin is changes due to the function of oestrous cycle expresses at the lowest level at pro-oestrus, which is the highest dioestrums.
The circulation of kisspeptin hormone level in blood is low in non-pregnant and in case of males; this increases very rapidly in the time of pregnancy. The level of this hormone falls down within five days of delivery. This implicates the source of this peptide is the placenta and it was found that there is a huge amount of kisspeptin in foteo-maternal interface. It is abundant in syncytiotrophoblast of both normal placenta of human and in pregnancy. As per the view of Kumar et al. (2014), reproduction can be controlled photo periodically where the kisspeptin during puberty make a modulator of similar type in photoperiodic control.
Reproduction was promoted for long days, again it was also inhibited...